In monitoring the heart action of a patient having a pacemaker, it is essential to positively identify the pacemaker pulses contained in the signals detected via body electrodes if the software programs used for analysis are to function properly. Falsely identifying other signal components as pace pulses is as undesirable as failing to identify the true pace pulses. Although the pace pulses generally have an amplitude that is greater than steady high frequency noise, identification on the basis of amplitude alone is not feasible because the amplitudes of motion and muscle artifacts and QRS waves are often as great or greater than the amplitude of the pace pulses. Identification of pace pulses on the basis of amplitude is further complicated by the fact that the baseline often drifts at a low frequency and the fact that the absolute amplitudes of the signals vary widely. Identification of a pace pulse on the basis of width holds little promise because the widths of the pulses supplied by different makes of pacemakers vary from tens of microseconds to 2.5 milliseconds. Identification of the pace pulses must be sensitive to both positive-going and negative-going pace pulses. For these reasons, prior art apparatus has not identified the pace pulses in a satisfactory manner.